1. Field of the Invention
The invention relates to devices for protecting the members of an aircraft crew against the effect of heavy accelerations which they may undergo for a short time during a mission (for example, when manoeuvring in aerial combat) or a prolonged time (for example, during the launching of a rocket for a space flight).
2. Description of the Prior Art
The prior art devices currently used for this purpose comprise a garment, or at least trousers, having pockets and a control member which supplies the pockets with compressed gas when the downwardly directed acceleration of the body exceeds a predetermined threshold, so as to prevent blood dropping to the lower part of the body, to the detriment of the supply to the brain. The most frequently used control member, known as an "anti-g valve", is formed by a valve controlled by an inertia block which controls admission to the pockets.
This well-established method provides satisfactory results, more particularly when it uses a valve having low inertia and when the response time is reduced by the pre-inflation of the pockets at altitude (French Patent Application No. 2 395 890). To further increase the capacities of the device, use has also been made of an electric control system using as pickup an accelerometer, possibly looped by a feedback signal supplied by a probe and representing the pressure in the pockets (French Patent Application No. 2 455 765).
In a general way the existing devices are adapted to set up an overpressure in the pockets only in response to an acceleration exceeding a predetermined threshold, usually equal to about 2g, such overpressure then being increased in accordance with a linear law as a function of acceleration. In this way, operation of the anti-g device and the consumption of gas can be prevented in the case of slight acceleration, corresponding to manoeuvres which the crew can well withstand, while at the same time avoiding the inconvenience of having the garments frequently applied tightly to the body by the over-pressurization of the pockets.
However, such a method has a basic disadvantage. The irritation suffered by the wearer of the garment will never be adequately compensated when the acceleration exceeds the threshold at which triggering takes place. It is more particularly an object of the invention to provide a device meeting practical requirements more satisfactorily than the prior art, and which combines satisfactory protection with comfort during low acceleration identical to that provided by the existing devices. To this end, the invention provides a device comprising means for controlling the pressure in the pockets in accordance with a law of increasing variation from a pressure level corresponding to a threshold value of acceleration, for example, about 1.8g.
A switch can be provided to enable the wearer of the garment to pass at will from the above law of variation to a law of pressure variation remaining uniform below the threshold; the curve of variation can more particularly be linear from a negative acceleration (i.e. directed towards the brain) up to a ceiling corresponding to the minimum value of tolerable overpressure in the pockets.
A device of the kind specified can be combined with means for pre-inflating the pockets and/or overpressurizing the supply of respiratory gas, for example, of the kind disclosed in French Patent Application No. 2 395 890.
The prior art anti-g devices have another basic defect. The pneumatic pressure set up in the pockets of trousers is uniform, while the acceleration applied takes the form of a hydrostatic increase in blood pressure, which increases in the direction of application of the acceleration (i.e. as a function of the level of the body of the individual). Consequently, devices intended to enable crews to withstand the accelerations occurring with high performance aircraft impose on the crews painful and tiring pressures to compensate the hydrostatic increase in the lower zones of the body. The fact that the pockets are not provided over the whole zone of the garment in contact with the limbs and that seams or folds are pressed into the muscles further increases the discomfort of the crews. It has been suggested to construct the pilot's seat so that he can stretch out, to reduce the height of the column of blood on which acceleration acts during flattening out or steep banking. However, this solution gives only small advantages, at the price of serious disadvantages.
Basically, one solution to the problems of giving protection against acceleration would consist in immersing the crew in liquid, acceleration causing a variation in the external hydrostatic pressure which compensates the effect on the blood at each level. In fact, centrifuge tests have shown an appreciable increase in tolerance to acceleration, enabling more than 15g to be tolerated for periods exceeding several minutes. However, it is clearly unrealistic to transfer this approach to an aircraft or space vehicle. Similarly, it appears at first sight that the use of a garment, or at least trousers having pockets subjected to hydrostatic pressure, is out of the question, since it would mean taking on board a considerable weight of water and the abandonment of the necessary pressurization during high altitude flying, implying the inhalation of respiratory mixture under pressure.
It is also an object of the invention to provide a device combining the advantages of protection ensured by a column of liquid subjected to acceleration and gas pressurization, more particularly the convenience of control by an anti-g valve, while substantially obviating the respective disadvantages of the two methods.